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Computer Science 324
Computer Architecture
Mount Holyoke College
Fall 2009
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Lecture 05: Adders
Date: Friday, September 25, 2009
- Announcements
- Lecture assignment recap
- Lab 1 recap
- Lab 2 out
- Encoder wrapup
- Adders
Circuit examples are in the shared area under "logisim".
Due at the start of class, Tuesday, September 29.
Turn in short answers to these questions. Please turn in a hard
copy (typeset or handwritten are OK). We will discuss these questions
during class, so no late submissions are accepted.
- Occasionally it is necessary to add 1 to a number, for
example, a program counter. Construct a device that is less expensive
than a ripple-carry adder, that adds one to a value that is provided
(D0..D3) and provides the result on the output (Q0..Q3). (Hint:
you may consider a modular approach.)
- Consider a 2-bit ripple-carry adder and a direct implementation
of a 2-bit adder using sum-of-products circuits (3 functions of 5
inputs). You need not construct the actual circuits, but discuss
the relative costs in terms of gate count and gate delay. How do
you think these change as the number of bits increases?